1. Field of the Invention
This invention relates to a picture displaying method whereby a picture corresponding to a picture display task switched among a plurality of the picture display tasks is displayed on a displaying device such as a CRT displaying one or the like.
2. Description of Related Art
Generally, a man-machine interface apparatus 6 as indicated in a block diagram of FIG. 1 consists of a CRT displaying device 1, a frame memory 2 for recording pixel information per a dot unit, a drawing controller 3 for drawing a picture into the frame memory 2, a microcomputer 4 incorporated with a multi-task operation: system and, a keyboard 5 for inputting data into the microcomputer 4 therethrough. The microcomputer 4 is connected with a controller 7 which holds the drawing data and controls the microcomputer 4.
FIG. 2 illustrates the constitution of tasks inside the microcomputer 4. There are three kinds of Dicture display tasks a,b and c as well as a picture switching control task d for controlling the activation and switching of the picture display tasks a-c. By way of example, if a key A (not shown) of the keyboard 5 is depressed, the picture switching control task d detects the depression thereby to activate the picture display task a. In consequence, the drawing controller 3 is turned intelligent, drawing a picture in the frame memory 2 on the basis of a drawing command from the microcomputer 4 (picture display task a), etc. The result is displayed on the CRT displaying device 1.
The operation of each picture display task a,b or c is shown in a flow chart in FIG. 3, and the procedure for the picture display (in the present instance, the picture dis1, play task a) will now be described with reference to this FIG. 3.
In the first place, a start demand from the picture switching control task d is waited for (step S1). When the start demand is extracted from the task d, a window is formed (step S2). In forming the window, the drawing area in the frame memory 2 is determined. Although it is possible to divide the screen into a plurality of sections thereby to draw a plurality of pictures simultaneously at one time, the whole of the Frame memory 2 is rendered one window in the present instance for brevity. Moreover, the picture display tasks a,b and c are allotted with the window Nos. 1,2 and 3, respectively. Therefore, a window forming command extracted from the picttare display task a reads as "Window forming (command), window No. 1--the drawing area is the whole area of the frame memory". Every drawing command extracted from the picture display task a is always added with the window No. 1 henceforward.
Secondly, a fixed picture is drawn (step S3). A group of drawing commands are extracted to display a fixed picture after a picture clear command is generated. The window No. 1 is added to the group of the commands. Since the window No. 1 has been already formed, the drawing controller 3 executes drawing into the frame memory 2 on the basis of the drawing commands. Then, the data held by the controller 7 are collected in communication with the microcomputer 4 (step S4). A group of drawing commands to display a variable picture are extracted on the basis of the collected data, with the window No. 1 added. The window No. has been aready formed and therefore, the drawing controller 3 executes drawing into the frame memory 2 as indicated by the drawing commands (step S5).
It is checked whether a task stopping demand is extracted from the picture switching control task d (step S6). Without the task stopping demand, it is returned to the data collecting step, thereby repeatedly collecting the data (step S4) and drawing a variable picture (step S5). On the contrary, with the task stopping demand extracted, the command directed to the window No. 1 is turned ineffective. Therefore, if the drawing command with the window No. extracted henceforth, the drawing controller 3 is regarded as in the error state without having formed the window. However, the drawing command to the window No. 1 is logically not extracted, and eventually the window is eliminated (step S7). Subsequently, a response to the task stopping demand is returned to the picture switching control task d (step S8). The flow is returned to the step S1 to wait for a start demand.
FIG. 4 is a flow chart indicating the operation of the picture switching control task d, based on which the proedure to switch the picture will be explained below. It is to be noted here that the following explanation is related to the case where a picture .beta. by the picture display task b which is currently being displayed is switched to a picture .alpha. through depression of the key A of the keyboard 5.
In general, it is in the waiting state for a picture switching demand (to wait for the key to be depressed) (step S11). When the key A is depressed, the waiting state is released, and a stopping demand is generated to the present picture display task b (step S12). A response from the task b is waited (step S13). When the response is generated, a start command is generated to the picture display task a (step S14), thereby returning to the waiting state again.
In this case, when the present task b is stopped, the picture switching control task d and picture display task b exchange messages therebetween. This is because the picture display tasks a and b might work at the same time unless the task a is started after the task b is completely stopped. In other words, the drawing command from the picture display task b would be carried out while a fixed picture corresponding to the picture display task a is drawn, resulting in the partial mix-up of the variable picture .beta. into the picture .alpha.. The messages are accordingly necessary to be exchanged between the tasks d and b in order to prevent the above-discussed mix-up.
Conventionally, the picture is switched in the manner as described hereinabove in the man-machine interface device. In the above-described manner, however, since the messages are exchanged between the picture switching control task d and picture display task a,b or c to stop the present task, it takes time to switch the picture. For example, when the stopping demand is generated at the very beginning of the collecting step of the data, it is impossible to respond to the stopping demand immediately until the variable picture is drawn. Collecting data and drawing the variable picture take several seconds, thereby decreasing the responding efficiency to switch a picture. Although may be considered to subdivide the data collecting process and the drawing process of the variable picture to frequently confirm the presence or absence of the stopping demand, the confirming process itself is a cause of the decrease of the responding efficiency to switch a picture.